Specs for using -C in combination with -e.

These specs test if using the -C option (to change the CWD) also work properly
when using the -e option.
Change CWD when using -C and -e together.

When one were to run `rbx -C X -e Y` Rubinius would not change the CWD to the
directory X. This patch fixes that so that behaviour is the same as when
running an existing script.
Merge pull request #2615 from rubinius/dash-upper-c-pwd

Changing CWD when using -C and -e